This article investigates the cost and feasibility of reducing U.S. greenhouse gas emissions by 80 percent from 2005 levels by 2050. The United States has stated in its Paris Conference of the Parties (COP) 21 submission that this is its aspiration. I suggest that this goal can be reached at a net cost in the range of $37 to $135 billion/year. I assume that the goal is to be reached by extensive use of solar photovoltaic and wind energy (66 percent of generating capacity), in which case the cost of energy storage will play a key role in the overall cost. I draw the tentative conclusion that a more limited use of renewables (less than 50 percent) together with increased use of nuclear power might be less costly.